Currently, Li-ion batteries have been applied in green vehicles, such as electric vehicles (EVs) and hybrid electric vehicles (HEVs). The workable voltage of a single cell in a Li-ion battery is approximately 3-4 volts, but EVs and HEVs usually require higher voltages up to more than 100 volts. Usually, multiple cells are coupled to each other in series to drive EVs and HEVs.
In battery management, a number of cells are arranged as one or more battery packs, and an analog front end (AFE) device is coupled to each battery pack to assess the status of the battery packs or the cells, such as their voltage and temperature. The digital data indicative of the status of the battery pack or the cells is transferred to a microprocessor for various purposes such as battery protection. A communication bus between the microprocessor and each AFE device is also needed.
FIG. 1 shows a conventional battery management system 100 with an opto-coupler based vertical bus. The AFE devices 122, 124 and 126 are coupled to the battery packs 112, 114 and 116, respectively, for accessing the status of each cell in the battery packs. Opto-coupler blocks 132, 134 and 136 establish a communication bus between the AFE devices 122, 124 and 126 and a central electronics control unit (CECU) 140. Each opto-coupler block includes two opto-couplers for each wire of the bus.
The conventional battery management system 100 with an opto-coupler based vertical bus suffers from high cost and high power consumption since opto-couplers are relatively expensive and their driving capability requires mille-amperes of current. Currently, a battery management system with a vertical bus in daisy chain architecture is widely used to reduce costs. However, communication between the AFE device and the CECU may be broken if there is a disconnect in the vertical bus in the daisy chain architecture. As a result, the reliability of the battery management system may be reduced.